1. Field of the Invention
The present invention relates to a control method for a robot apparatus and a robot apparatus for protecting a power supply unit in the robot apparatus utilizing an articulated arm to be driven by controlling a plurality of joints.
2. Description of the Related Art
In the past, robot apparatuses have been developed each having an articulated arm having a plurality of joints. An articulated arm utilized in such a robot apparatus may internally contain an actuator such as a motor in each of joints, and a driver (substrate) for controlling an operation is connected to each of the actuators. A power supply cable and a signal cable are connected to each of the drivers. The power supply cable is usable for supplying driving power from a power supply body, and the signal cable is usable for transmitting/receiving a control signal to/from a control device. Here, the part from the power supply body to the driver which receives driving power, that is, the power supply body, the power supply cable, the connector and so on will be collectively called a power supply unit.
In recent years, such robot apparatuses each including an articulated arm are increasingly being utilized for works such as automatic assembly works. In this case, because such an assembly work may require a high speed operation, the steep acceleration and deceleration of joints may be required for higher speed operations of the articulated arm. However, in order to achieve steep acceleration and deceleration of joints, a higher motor output may be required, which imposes an overload on the power supply unit and may possibly cause a malfunction of the articulated arm.
Furthermore, a reduced size of the power supply unit may prevent supply of power required for the articulated arm to operate, which may also impose an overload on the power supply unit. In this case, the articulated arm may operate at a required speed, which may also possibly impose a mechanical overload on joints.
In order to prevent such overloads on the power supply unit due to a larger amount of power required in such articulated arm than the power of the power supply unit, control over the articulated arm may be demanded such that a load on the power supply unit may be equal to or lower than an allowable value set based on performance of the power supply unit. U.S. Pat. No. 7,023,164 proposes an over-current protection device which includes a sensor for measuring an actual load acting on a power supply unit while an articulated arm is operating and detecting an overload by comparing the measured value and a threshold. In the overcurrent protecting apparatus, if the measured value is higher than the threshold, the robot apparatus is powered off immediately. This overcurrent protecting apparatus shuts down the robot apparatus if it is determined that an overload is imposed on the power supply unit such that a malfunctioning articulated arm may be prevented from continuously operating.
However, the overcurrent protection device disclosed in U.S. Pat. No. 7,023,164 may require immediate execution of a protection operation and shut down when occurrence of an overload is detected because a load on a power supply unit is measured after an articulated arm starts operating. This may possibly influence on an operation takt time of the robot apparatus.